1. Field of the Invention
The present invention relates to a magnetically driven agitator.
2. Brief Description of the Related Art
Agitators are conventionally used for stirring a mixture contained inside a recipient in order to avoid a decantation or any other alteration of the mixture in the course of time. A magnetically driven agitator presents the advantage that the propelling screw that it comprises is set in motion by a magnetic coupling which takes place without physical contact between two rotating parts, such as the driven shaft of an electric motor and the propelling screw which is associated therewith. This makes it possible to dispose this shaft outside the recipient while the propelling screw is installed inside the recipient. Any danger of leakage at the level of the agitator may thus be set aside. This is particularly useful when the mixture is toxic or when pollution thereof by outside agents must be avoided, such as for example in the case of a medicinal composition.
In the known devices, this absence of mechanical connection between the drive shaft and the propelling screw may lead to errors in manipulation or blockages which cannot be revealed before the recipient is completely emptied. For example, an operator may forget to install the propelling screw inside the recipient while the shaft for moving the propelling screw is rotating normally, and one might be led to believe that the agitator is performing its function. As a mixture can be stirred for a relatively long period of time, of the order of several days and even of several weeks, if this omission is discovered at the end of manipulation, numerous working hours are lost, as well as a high value-added product. Similarly, it may happen that a propelling screw is jammed, particularly due to the non-homogeneous nature of the mixture contained in the recipient. Such a jamming is not detected by a corresponding jamming of the shaft since the latter is not mechanically connected to the propelling screw.
In order to overcome the problems set forth above, it may be envisaged to install a sensor, for example a capacitive one, in the vicinity of the agitator. The installation of such a sensor would require an additional bore in the wall of the recipient, which would increase the risks of leakage and poor cleaning and would necessitate precise operations for positioning and adjusting this sensor with respect to the propelling screw inside the recipient, i.e. in a zone of reduced access. This would result in the device being overpriced.
It is a particular object of the invention to overcome these drawbacks by proposing a magnetically driven agitator in which a defective rotation of the propelling screw can be immediately detected without it being necessary to make additional bores in the wall of the recipient.